DPF systems in which PM discharged from a diesel engine is trapped by a filter called DPF to reduce a quantity of PM discharged to the outside are known. As an example of such DPF systems, ones using a continuously regenerating DPF device including a DPF and a DOC (diesel oxidation catalyst) provided on the upstream side of the DPF are known.
In a continuously regenerating DPF device, if a temperature of an exhaust gas is approximately 350° C. or higher, PM trapped by the DPF is continuously burned for purification, whereby the DPF is self-regenerated; however, if the temperature of the exhaust gas is low, a temperature of the DOC is lowered and the DOC is not activated, and thus, it is difficult to oxidize PM to self-regenerate the DPF. As a result, PM is accumulated in the DPF and clogging of the DPF is thereby developed, causing the problem of an increase in exhaust pressure.
Therefore, in DPF systems, DPF regeneration is implemented, in which when a quantity of PM accumulated in a DPF exceeds a predetermined quantity, multi-stage delayed injection (multi-injection) and subsequent injection (post-injection) of fuel in a cylinder (tube) is performed to forcibly increase a temperature of an exhaust gas flowing into the DPF to burn and remove the PM trapped in the DPF.
The multi-stage delayed injection (multi-injection) is performed to raise the temperature of the exhaust gas emitted from the engine to raise a temperature of a DOC to a catalyst activation temperature. Also, the subsequent injection (post-injection) is performed to supply a large quantity of unburned fuel into the exhaust gas to oxidize (burn) the supplied unburned fuel by means of the DOC, whereby the temperature of the exhaust gas at an entrance of the DPF is raised to a temperature equal to or exceeding a temperature at which PM is burned.
Types of the DPF regeneration include automatic regeneration and manual regeneration. Automatic regeneration refers to DPF regeneration that is automatically performed while the vehicle is moving, and manual regeneration refers to DPF regeneration that is manually performed via the driver's operation during the vehicle being stopped.
During DPF regeneration, as described above, post-injection is performed, and thus, a phenomenon called oil dilution in which an unburned fuel is mixed into an engine oil (lubricating oil) to dilute the engine oil occurs.
In automatic regeneration in which DPF regeneration is performed while the vehicle is moving, the load on the engine is not stabilized and thus, the exhaust gas temperature is not stabilized. Accordingly, in order to reliably increase the exhaust gas temperature at the entrance of the DPF, the post-injection quantity is set to be somewhat larger. Thus, in automatic regeneration, the dilution quantity, which is a quantity of fuel mixed into the engine oil, is large. Meanwhile, manual regeneration in which DPF regeneration is performed during the vehicle being stopped, the exhaust gas temperature is stabilized and thus, the post-injection quantity can be set to be small, enabling the dilution quantity to be reduced.
The dilution quantity is reduced by making the vehicle move, thereby volatilizing the fuel mixed in the engine oil; however, if a regeneration interval from an end of DPF regeneration to a start of DPF regeneration is short, the dilution quantity is continuously increased rather than being reduced, which may cause a failure.
Therefore, DPF systems are configured to, on condition that when a quantity of PM accumulated in a DPF exceeds a predetermined quantity, an accumulated dilution quantity is smaller than a predetermined threshold value and the regeneration interval is equal to or exceeds a predetermined threshold value, perform automatic regeneration, and if the aforementioned conditions are not met, urge a driver to perform manual regeneration to perform manual regeneration via the driver's operation during the vehicle being stopped.
Also, as one of types of DPF regeneration, there is LLIR (long low idle regeneration), which is performed when an idle state continues for a period of time equal to or exceeding a predetermined period of time (see, for example, patent literature 1).
In LLIR, an accumulated PM quantity in an idle state is estimated, and when the estimated accumulated PM quantity exceeds a predetermined quantity, manual regeneration is automatically performed.